As earlier we discuss that IPv6 is the improved version of the internet protocol. The IPv6 header is one of the major improvements over IPv4 header. The header format has been greatly simplified for. Some of the header fields have been removed and others have been moved to the optional IPv6 Extension Header. The IPv6 header is only twice the size of the IPv4 header because the IPv6 address is 128 bit.

The IPv6 Header has greatly evolved from its IPv4 predecessor. The header of IPv6 is larger but takes up a smaller percentage of the overall header space. Some fields, for example; the Options Field and Header Checksum have been removed and replaced with improved functions in the IPv6 Extension Header. The IPv6 Header was designed to facilitate routing efficiency.

IPv6 Header Format

The improved and simplified IPv6 header as shown in Figure 1 consists of 40 octets (largely due to the 128 bit both of the source and destination IPv6 addresses) and 8 header fields (3 IPv4 basic header fields and 5 additional header fields). As painted int the figure, some fields have kept the same names as IPv4, some fields have changed names or positions, and a new field has been added.

In contrast, the IPv4 header shown in Figure 2 consists of 20 octets (up to 60 bytes if the Options field is used) and 12 basic header fields, not including the Options field.As painted in the figure, for IPv6, some fields have remained the same, some fields have changed names and positions, and some IPv4 fields are no longer required.